Two incidents in particular raised red flags. In one case in 2007, an agent was arrested for public intoxication. The other incident occurred last year, when police handcuffed and temporarily detained two agents after an incident at a bar.

"Alcohol incidents such as these, as infrequent as they may be, indicate a potential vulnerability in OST's critical national security mission," the report warns.

The report did not identify the locations for either incident, nor did it say whether the agents were fired.

The Energy Department's National Nuclear Security Administration, which oversees the 600 agents, stressed that the report found no evidence of them driving drunk while on duty or of a systemic problem.

"NNSA's Office of Secure Transportation maintains a highly trained, highly professional force that has safely and securely transported nuclear materials more than 100 million miles without a single fatal accident or any release of radiation," said NNSA spokesman Damien LaVera.

"Of hundreds of agents," he added, "the report identifies just two cases involving NNSA personnel being intoxicated while on overnight stops during official missions."